The objectives are to determine whether findings of cross-sectional age differences correspond to longitudinal changes in memory and cognition in older adults and to evaluate hypotheses regarding cognitive changes. Considerable effort has been devoted to identifying the mechanisms of change, yet it is not completely clear how memory and cognition changes in individuals as they age. The significance of the present research program is that it charts longitudinal memory change, it assesses individual differences in change, it uses multiple measures of all cognitive constructs and growth models to analyze the data, and it includes evaluation of mortality, practice, and attrition on change. The study uses a multi-sample sequential design with adults ranging in age from 30-97 and follows them at 3 year intervals. Longitudinal changes are compared with change estimates from cross-sectional samples to evaluate the effects of age and cohort. Cohort-sequential modeling makes it possible to evaluate the external validity of cross-sectional designs in estimating memory change. The role of individual differences in memory performance is investigated through analyses of changes in memory predictors including psychometric abilities related to fluid and crystallized abilities, working memory, speed, and other abilities, as well as demographic characteristics including gender, education, health, and affective status. In addition, 25 percent of LBLS subjects will be randomly selected to complete the cognitive measures of the Health and Retirement Study (MRS), a population sample of American adults over age 50. The hypotheses tested are that longitudinal findings assess age changes in memory and cognition more accurately than cross sectional ones;that cohort effects account for many of the age effects observed in memory and cognition, but not at the end of the life span due to selection in very old age;that there is structural invariance longitudinally in the factors measured, but that different tasks are differentially predicted by factors because of task demands;and that younger cohorts, as exemplified by the Baby Boomers, may experience fewer negative effects of cognitive aging than their predecessors. Results of this research will not only provide answers to important methodological questions regarding change in memory, but they also address a number of issues related to individual differences in intraindividual change in cognition, and suggest possible mechanisms of change in healthy older adults. People are concerned about their mental abilities, an important aspect of health and well-being, as they get older. This research focuses on age changes in ability to think, remember, reason, use language, and make plans: what changes are normal, whether there is one particular age where changes occur more rapidly, what changes are due to health problems, and whether the baby boomers will experience fewer changes in their mental abilities.